This is a application for a double blind, placebo-controlled study to determine if vitamin C supplementation (500 mg daily) can decrease the effect of maternal smoking in pregnancy on offspring pulmonary function (VC-SIP). Smoking during pregnancy remains a major public health problem as at least 12% of pregnant women cannot quit smoking during pregnancy. This addiction is the largest preventable cause of childhood respiratory illness, including asthma, and children whose mothers smoked during pregnancy show lifetime decreases in pulmonary function. Smoking is a unique morbidity in that it is addictive, heavily advertised and recent genome studies show there are genotypes that significantly increase the likelihood of being unable to quit. Teen pregnancy, low income, low education, and living with another smoker are important factors increasing the odds of smoking during pregnancy. Pulmonary function tests done shortly after birth in babies born to mothers who smoked during pregnancy show decreased pulmonary function as measured by decreased respiratory flows and compliance and altered tidal breathing patterns. These changes can still be measured even after the infants have reached adulthood. Multiple epidemiologic studies show that these decreases in pulmonary function lead to increased respiratory disease and costs of hundreds of millions of dollars per year. The primary aim of this multi-site study is to demonstrate improved pulmonary function testing at 3 months of age, in infants delivered to smoking mothers who are randomized to 500 mg/day of supplemental vitamin C versus placebo prior to 22 weeks of pregnancy. Patients will meet with research personnel at each prenatal visit and smoking cessation will be actively encouraged. Patients will be monitored with a set of serial biomarkers to assess smoking and medication compliance, including urine cotinines levels, smoking questionnaires, pill counts and fasting plasma ascorbic acid levels. Pulmonary function tests will be done at 3 months of age and will measure forced expiratory flows. Success of this study is supported by strong pilot data from Dr. McEvoy's K23 showing statistically significant improvements in pulmonary function tests in infants born to smoking mothers who received vitamin C, and preliminary data showing a lower incidence of wheezing at 1 year of age in these infants. Key genetic polymorphisms shown to increase sensitivity to in utero smoke exposure will also be measured. The success of this study is also supported by animal models showing the effectiveness of vitamin C to preserve pulmonary function and genetic and epidemiologic studies linking the effects of smoking during pregnancy to oxidant mechanisms. Given nicotine's addictive nature, the underserved socio-economic nature of the patient population, and the constant advertising by tobacco companies, smoking during pregnancy will continue to adversely victimize millions of babies worldwide. This research has great public health significance to potentially alter the fetal origins of respiratory disease by blocking some of the effects of in-utero smoke exposure on lung development.